Former Tulsa County District Attorney Tim Harris and businessman Kevin Hern will advance to a Republican primary runoff for Oklahoma’s open 1st District seat.

None of the five GOP candidates won a majority in Tuesday’s primary. With 100 percent of precincts reporting, Harris led with 28 percent to 23 percent for Hern, according to the Associated Press.

The two will face off on Aug. 28 for the seat left open by GOP Rep. Jim Bridenstine, who resigned in April to become NASA administrator. The seat will remain vacant until November, when the winner of the general election will serve out the remainder of his term.

Whoever wins the runoff in the Tulsa-anchored district is expected to be in a strong position in November. Inside Elections with Nathan L. Gonzales rates the race Solid Republican.

The conservative Club for Growth PAC had endorsed former military intelligence officer Andy Coleman, who came in third. Hern had loaned his campaign $700,000 and spent more than $1 million on the primary.

Democrats Tim Gilpin and Amanda Douglas will compete in the Aug. 28 runoff for the Democratic nomination.